Zika Test Yields False Positives as Brazilian Women Continue to Avoid Pregnancy


Today, the US Food and Drug Administration (FDA) released a safety document cautioning healthcare providers from relying solely on commercial IgM Assay results when diagnosing Zika, as false positives have been observed.

Today, the US Food and Drug Administration (FDA) released a safety document cautioning healthcare providers not to rely solely on commercial IgM Assay results when diagnosing Zika, due to the fact that false positives have been observed.

The ZIKV Detect IgM Capture ELISA test is used “for the preliminary (presumptive) detection of Zika virus IgM antibodies in human sera.” This test was previously recommended by the Centers for Disease Control and Prevention (CDC) to only be used in patients who exhibit Zika-like symptoms, or those who have a history of travel to a Zika-endemic region.

Now, the FDA has announced that false positives were reported by Laboratory Corporation of America (LabCorp). However, further investigation is needed before confirming the relation between the false positive results and this test. While the FDA states that using IgM tests to diagnose Zika are still useful, physicians should not use them as the sole means of diagnosis and should not base treatment plans on the outcomes of these tests. This test was manufactured with the intent of preliminary diagnosis, and so, confirmatory tests are recommended. However, confirmation of Zika diagnosis may take from one week up to one month. Nonetheless, since there is a “higher likelihood” that the ZIKV Detect test may yield false positives, the FDA urges physicians to wait for confirmation results “before making patient management decisions.”

According to the FDA press release, “After transitioning to the ZIKV Detect test, LabCorp observed higher than expected false positive results. The CDC confirmed less than half of those presumptive positive results captured by LabCorp through the ZIKV Detect test.”

Although confirmation testing may take up to a month, samples collected from pregnant women will be prioritized. Patients who test positive with the ZIKV Detect test should be informed of the probability that they may not, in fact, be infected with the Zika virus, so as not to make any decisions based on misguided information, the FDA noted.

LabCorp, the CDC, the FDA, and InBios, the manufacturer of the ZIKV Detect test, are currently working together to “identify the root cause of the problem.” In response to the ramifications of the Zika virus, the CDC has awarded $184 million to states, territories, local jurisdictions, and universities to continue preventive Zika efforts nationwide. This funding comes from the Zika Response and Preparedness Appropriates Act of 2016, which granted the CDC $350 million.

The total of $184 million will be distributed as follows:

  • $25 million will go towards protecting areas at greatest risk of local Zika transmission that may result in outbreaks
  • Approximately $97 million will go towards state, local, territorial, and city health departments
  • Approximately $8 million will go towards microcephaly and birth defect surveillance
  • Approximately $40 million will be awarded to four universities to fund emerging and exotic vector-borne disease centers, such as Zika, in the United States
  • Approximately $14 million will go towards creating a Vector Control Unit in Puerto Rico, the highest Zika-prevalence region in the United States

Meanwhile, in Brazil, a group of researchers are calling for government officials to reconsider the legal ramifications of abortion in a letter to the editor of the Journal of Family Planning and Reproductive Health Care. They report that 56% of women in Brazil are avoiding pregnancy due to the Zika epidemic. This comes as no surprise, since, according to the Pan American Health Organization, Brazil has reported 109,596 locally-acquired cases of Zika virus infection since Zika was first reported to have been circulating in the country. Not only this, but 2,228 fetuses and infants were confirmed to have been affected by congenital Zika virus syndrome since 2015.

Although Zika virus is no longer considered to be a public health emergency of international proportion, it is still a great threat to pregnant women and their developing fetuses. As time progresses, we continue to learn more about the complications Zika can cause during congenital infection. It is for these reasons that continued surveillance and diagnostic and prevention efforts are imperative.

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